Abstract

The production of high quality timber from hardwood requires a gentle and controlled drying to a low wood
moisture content. While ambient air drying depends on the weather conditions, conventional hightemperature
dryers cause high investments and energy costs. Up to now, solar dryers could not be
established in industrial timber production, due to their insufficient drying capacity and the lack of an
adequate control of the drying conditions.&lt;br&gt;
Therefore, a new solar dryer was developed, which allows a controlled drying of up to 250 m&lt;sup&gt;3&lt;/sup&gt; of timber
per load. The frame of the dryer is covered with a transparent, highly UV-stabilised and well isolating air
bubble foil. A specially developed microprocessor control regulates air flow, temperature, humidity and
a back up wood chip furnace, which provides the heat during night and unfavourable weather conditions.
The drying regime is adjusted automatically according to the type of wood, the board thickness and the
ambient air temperature.&lt;br&gt;
The paper presents the experiences gained during the operation of the two worlds largest solar timber
dryers, drying up to 35000 m&lt;sup&gt;3&lt;/sup&gt; of eucalypt annually. The investigations showed, that investments, drying
costs and energy consumption could be reduced by 50 % compared to conventional high-temperature
drying systems. At the same time the quality of the timber was improved considerably.